My inspiration for this project came from a balloon organ I saw at Maker's Faire in Austin, TX. What I saw was a fairly small organ made from PVC with compressed air and a balloon vibrating membrane. What I remember of that stuck with me and I eventually found a video of Fran Holland's copper piping balloon organ. I just scaled that up to a much larger level. I initially used this as a stationary noise maker but this year, I adapted it to a more portable format powered by CO2 paintball tanks.
I should mention a little bit about SAFETY. Compressed air can be dangerous. Wear eye protection. If using CO2, it is even more risky as the tanks used contain much higher pressure. You could get frostbite from a rapidly discharging tank should something go wrong. You should use as little air pressure as you can to get whatever desired effect you're looking for. The membrane heads (and hose clamps) WILL FLY OFF if you send way too much air pressure to them all at once and they will hurt if they hit you. Use an air pressure regulator on your air compressor or be very careful using a CO2 tank (with multiple valves). For CO2 tanks, the best I could do at regulating air pressure was to just barely crack the pin valve so that the least amount of gas flow was enabled and mid-hose was a heavy duty ball valve. I don't (yet) go into much detail about your air supply, but just be careful.
Step 1: How It Works
Compressed air could come from an air compressor (used for air tools) or a portable CO2 tank (as used in paintball). Each has its strengths and weaknesses. The compressed air is preferable if your setup is stationary. Most air compressors come with a regulator built in that you can easily lower down to around 30-50psi. A 10gal air tank will make about 1 minute of noise before the compressor kicks in to start refilling the tank. Conversely, a 20oz CO2 tank will last roughly 3-4 minutes.
As for the design of the air column, I've used a 6ft straight pipe for the loudest, deepest effect. The portable version includes a 180deg turn with a 90deg turn at the end for aiming purposes. This is nowhere near as loud, but makes sense for portability.
There are several grades of PVC. The heavy grade stuff will cost you a lot more money but will be much louder. Lighter PVC (used for sewage/drainage) is better for portable applications as it is MUCH lighter. There are techniques on the internet that describe how to bend PVC using heat application. I don't go into those here, but they are easy enough to find online. Tapping the holes for the air hose adapters may be more of a challenge with the thinner PVC.
Step 2: Gathering the Parts
Air column tubing:
4" pvc tubing about 6' long for stationary. Build to suit for portable version.
Resonator section PVC:
3" down to 2" reducer. Make sure it fits inside of the 4" tubing. I had to Dremel mine a little bit if I recall correctly.
Large hose clamp to fit around 4" tubing
Air hose adaptors
Air hose "T" splitter
Air valve for compressed air version:
Use automated water sprinkler valve for <90psi air. This valve requires several adapters to get it down to 1/4" air tubing.
Air valve for CO2 version:
use a heavy duty ball valve. No normal/cheap air regulator will work with CO2 due to the high pressure.
This one may take some trial and error. I went with a hybrid material found at my local hardware store. You want it thin but tough. It should have some elasticity but not so much that it fails after only a little bit of use.
Step 3: The Resonator Head
Drill and tap a hole in the side of the main "Y" PVC piece. Make sure that it's positioned above where the 3"-2" reducer narrows (see image below).
Position the membrane material over the whole top and place a hose clamp over it to lock it down. Pull on the edges of the membrane after lightly tightening the hose clamp to make it taught. Once it's relatively smooth around the edges, tighten the hose clamp enough to secure it but not enough to damage the material.
The resonator head should be ready at this point. If you have a "Y" section, repeat for the second opening.
Step 4: Air Supply
The portable setup can use CO2 (such as from a paintball gun). You must use a ball valve with CO2 instead of a check valve. Most regular air tools will fail under the much higher psi of a CO2 tank. The ball valve is the only mechanism that I didn't destroy in the process of setting up the CO2 tank.
Step 5: Stationary Version
Step 6: Portable Version
I also zip tied a small camelbak backpack to it and taped a loop for a belt to the bottom. This was relatively comfortable. I had to use a separate adaptor system for the CO2 tank that was borrowed from a friend's paintball equipment.